This invention relates to the operation of internal combustion engines and, more specifically, to a system for starting and warming internal combustion engines with a gaseous, typically short chain hydrocarbon, fuel.
Emissions of hydrocarbons, carbon monoxide and other gases from internal combustion engines are a major contributor to poor air quality, smog and the like. Great efforts at high cost have been made to reduce such emissions. Among these are the use of catalytic converters to reduce emissions in the exhaust system, computer control of engine operation and special, more costly, gasoline blends. One of the major remaining contributors to engine generated air pollution is the greatly increased hydrocarbon and carbon monoxide levels generated during engine starting and warm-up, especially under cold ambient conditions. Catalytic converters must reach a minimum temperature, generally about 400.degree. F. before they can effectively eliminate pollutants such as unburned hydrocarbons, carbon monoxide, and nitrous oxides. It has been estimated that during a typical 20-minute drive over half of the total undesirable emissions are generated during warm up and that about 70 to 80 percent of total vehicle emissions produced during the Federal Test procedure cycle are emitted within the first two minutes of cold start.
Large amounts of unburned gasoline pass to the exhaust system during the period before catalytic converter warm-up occurs. In very cold conditions the engine may turn over for quite awhile before it "catches" and begins to run. Engines often run roughly when cold, intermittently missing and passing high levels of hydrocarbons and carbon monoxide to the atmosphere during this warm-up period. Air/fuel ratios of one-to-one with liquid fuels at low temperature start-up with very little vaporization are typical. Diverter systems and electrically heated catalytic converters have been suggested to reduce this burst of start-up and warm-up emission. Electrically heated converters and diverters with gas traps add undesirable cost and weight to the system. Electric converter heaters are not fully effective in eliminating undesired emissions during catalytic converter warm up periods since the catalytic converter is not uniformly heated by the proposed electrical heaters. Further, there is a significant time delay between the time an electrical heater is turned on and the catalytic converter is heated to the required temperature. In order to be effective, the driver must turn on the heater and wait until the catalytic converter is heated before starting the engine. In addition, these heaters draw high current and may run the battery down so far as to making starting after the catalytic converter is heated difficult or impossible.
When gasoline is injected into cylinders which do not immediately fire, that gasoline washes oil off of the cylinder walls, reducing lubrication between piston rings and cylinder walls, increasing wear and significantly reducing engine durability. Also, some of the gasoline will bypass the piston rings and contaminate the engine oil, reducing the lubrication efficiency of the oil and requiring more frequent oil changes.
The irregular ignition during starting also reduces spark plug life and increases carbon deposits. The longer starting procedures will increase starter, ring gear and battery wear, again reducing long term engine durability. Under very cold conditions, battery capacity is inherently reduced, so that the battery may not be able to continue to operate the starter if the engine does not start immediately.
A system is described by Wilson in U.S. Pat. No. 5,184,585 for adding a volatile fuel, such as butane or propane, to a liquid fuel, such as gasoline or diesel fuel, when starting an internal combustion engine at low temperatures. While this system will aid in starting under difficult starting conditions, it will do little, if anything, to prevent pollutants from the liquid fuel component, such unburned hydrocarbons, carbon monoxide and the like, from passing through the cold catalytic converter into the environment.
Hutchinson, in U.S. Pat. No. 3,799,125, describes a complex and expensive system for stripping volatile components from gasoline fuel and using those components for starting and warming a gasoline engine. However, the mixture of volatile components will still produce unburned hydrocarbons, carbon monoxide and other undesired components which will pass through the cold catalytic converter and into the environment. Present day gasolines and diesel fuels are carefully formulated blends of many components to produce acceptable performance with reduced pollution. If many short trips are made under low temperature, winter conditions, the remaining liquid fuel in the tank will gradually increase in heavy, less volatile components which are not an efficient fuel in the absence of the normal proportion of the more volatile components. Hutchinson further teaches that it is impractical to use vaporized LPG fuel during the engine warm-up period, typically 2-3 minutes, then switch to liquid fuel.
Thus, there is a continuing need for improvements in starting internal combustion engines, especially in cold conditions, to reduce hydrocarbon and carbon monoxide emissions during the catalytic converter warm-up period, reduce the size and cost of the required catalytic converter, increase engine durability and assure rapid engine starting.